BIRDS. 205 
this is the case, the young of both sexes resemble the female. When 
the adult male and female are of the same colour, the young ones have a 
livery peculiar to them, 
The brain of Birds has the same general character as that of other 
Oviparous Vertebrata, but it is distinguished by its very great propor- 
tionate size, which often surpasses even that of this organ in the Mamma- 
lia. This volume principally arises from tubercles, which are analogous 
to the corpora striata, and not upon the hemispheres, which are narrow 
and without convolutions. The cerebellum is tolerably large, and almost 
without lateral lobes, being chiefly constituted by the vermiform process. 
The rings of the trachea in Birds are entire; there is a glottis at its 
bifurcation most commonly furnished with peculiar muscles, which is called 
the inferior larynx; this is the point where the voice of birds is pro- 
duced; the immense volume of air contained in the air sacs contribute to 
its strength, and the trachea, by its various forms and motions, to its mo~ 
difications. The superior larynx, which is extremely simple, enters the 
inferior, but has little to do with the voice. 
The face, or upper mandible of Birds, consisting chiefly of their inter- 
maxillaries, is lengthened out behind into two arches, the internal of 
which is composed of the pterygoid and palatine bones, and the external 
of the maxillaries and jugals, both of which rest on a movable tympanic 
bone, commonly called the square bone, analogous to that of the drum of 
ear; above, this same mandible is articulated with the cranium, or united 
to it by elastic lamine, a kind of union which always allows the parts 
some degree of motion. 
The horny substance which invests the two mandibles, performs the 
office of teeth, and is sometimes so jagged as to resemble them; its form, 
as well as that of the mandibles which support it, varies extremely, and 
according to the kind of food used by each species. 
The digestion of Birds is in proportion to the activity of their life, and 
the force of their respiration. The stomach is composed of three parts: 
the crop, which is an enlargement of the cesophagus; a membranous sto- 
mach, in the thickness of whose parietes are a multitude of glands whose 
juices moisten the food; and finally, the gizzard, armed with two power- 
ful muscles, and united by two radiated tendous, which are lined inter- 
nally with a cartilaginous kind of velvet. The food is the more easily 
ground there, as birds constantly swallow small stones, in order to increase 
their triturative power. 
In the greater part of the species which feed exclusively on flesh or 
fish, the muscles and villous coat of the gizzard are greatly attennated ; 
and it seems to make but a single sac with the membranous stomach. 
The dilatation of the crop is also sometimes wanting. 
